import java.applet.*;
import java.awt.*;

public class ComponentUpdating extends Applet 
  {
    public void init () 
      {
        Panel panelOne = new SubPanel(Color.lightGray, Color.white);
        Panel panelTwo = new SubPanel(Color.yellow, Color.black);
        setLayout(new GridLayout(0,1));
        add(panelOne);
        add(panelTwo);
      }
  }

class SubPanel extends Panel 
  {
    private boolean toggle = false;
    private Color color1;
    private Color color2;
    public SubPanel(Color c1, Color c2) 
      {
        color1 = c1;
        color2 = c2;
      }

    public void paint(Graphics g) 
      {
        if (toggle) g.setColor(color1);
        else        g.setColor(color2);
        Rectangle bounds = getBounds();
        g.fillRect(0, 0, bounds.width, bounds.height);
        toggle = !toggle;
      }
  }